This invention relates to a vehicle constant-speed cruising device.
A vehicle constant-speed cruising device has been disclosed by Japanese Patent Publication Sho-58-39311 (1983). In such a device, when a vehicle is running at a constant speed that is desired to drive the vehicle, that speed is set as a target speed. Thereafter, the vehicle is controlled to run at the target speed. The vehicle speed is controlled as follows. A difference signal between the target speed signal and a traveling speed signal is amplified by a predetermined gain. And, an acceleration signal is also amplified by a predetermined gain. Then, the two amplified signals, the difference signal and the acceleration signal, are calculated to obtain a throttle valve driving signal The signal thus obtained is applied to an actuator, to cause the travel speed to reach the target speed.
In the above-described conventional device, because of the cable-layout hysteresis of the vehicle, the driving amount of the throttle valve is varied whether a signal applied to the actuator is the acceleration or deceleration. That is, since the throttle valve and the actuator for driving the throttle valve, such as an electric actuator or a pressure actuator, are mechanically connected by a wire cable, a force to open the throttle valve is required larger than a force to close the throttle valve due to a return spring of the throttle valve, friction of the wire cable, or the like. Thus, the cable-layout hysteresis is caused. Therefore, it is difficult to maintain the vehicle speed at constant. And, it is difficult to rapidly converge the vehicle speed at the target speed.